Embryology Flashcards
The development of what systems are linked?
Urinary, GI and reproductive
What are the 2 avascular membranes after gastrulation?
Buccopharyngeal membrane
Cloacal membrane
Where do the kidney and to go ad form from?
Intermediate mesoderm at the urogenital ridge
What is the first sequential system in the development of the UT and where does it develop?
Pronephros in the cervical region
What happens to the pronephros?
It is never functional but it produces the pronephric duct which extends from the cervical region to the cloaca and drives the development of the next developmental stage - becoming the mesonephric duct.
What happens to the mesonephric duct?
It sprouts mesonephric tubules that develop caudal to the pronephros region. Duct + tubules = embryological kidney.
It then sprouts the ureteric bud which induces development of the definitive kidney and aids development of the male reproductive system.
What happens to the ureteric bud?
It expands and branches into the undifferentiated intermediate mesoderm (metanephric blastema)’forming the kidneys structure.
When do each sequential structures appear and regress during the development of the urinary system?
Pronephros - start of week 4 to end of week 4
Mesonephros - end of week 4 to end of week 8
Metanephros - week 5 (functional from end of 1st trimester)
Where does the metanephric kidney appear and what happens to it?
Appears in the pelvic region. Undergoes apparent caudal to cranial shift, crossing the arterial fork formed by vessels returning blood from the foetus to the placenta. Kidneys don’t actually move but the trunk moves downwards.
What is renal agenesis and what is a sign of it?
When the ureteric bud fails to interact with the intermediate mesoderm (one or both kidneys). Bilateral shown by low amniotic fluid (no foetal urine)
What is a horseshoe kidney?
During the kidneys ascent, they lie close to each other. If they both get caught on the arterial fork (IMA) they can fuse and form a horseshoe kidney. Located at the pelvic brim.
What is the potential consequence if the ureteric bud splits?
Ectopic opening (into vagina or urethra) leading to incontinence.
How do accessory renal arteries form?
Arterial supplies remain as the kidney ascends and obtains new vessels. These are end arteries.
What is the cloaca?
The end of the GI, urinary and reproductive tracts early in development. It is a dilated blind pouch separated from the outside by the cloacal membrane.
Where does the bladder develop from?
The hindgut
How is the cloaca divided?
By the urorectal septum into the urogenital sinus (future bladder and urethra) and anorectal canal.
What is the allantois and what happens to it?
A supraventral diverticulum of the hindgut that extends into the umbilical cord. The lumen becomes obliterated to become the Uracus - the median umbilical ligament in adults.
Describe the parts of the urogenital sinus
Upper - future bladder
Pelvic - future preprostatic, prostatic and membranous urethra
Phallic - future spongy urethra in males
Describe the development of the male bladder
Mesonephric ducts reach urogenital sinus
Ureteric bud sprouts from mesonephric duct
Urogenital sinus begins to expand and smooth musculature begins to appear (future trigone)
Ureteric bud and mesonephric ducts make independent openings in the urogenital sinus
Prostate and prostatic urethra (from narrowing UGS) are formed.
Mesonephric ducts form the prostate and ducts of the male reproductive system
How does female bladder development differ from that of males?
Without male hormones the mesonephric duct regresses (no prostate or male reproductive organs)
What is exstrophy of the bladder?
When part of the bladder is outside of the body due to maldevelopment of the lower abdominal wall or urachal fistula (patent uracus).
What is hypospadias?
A defect in the fusion of urethral folds. Urethra opens onto the ventral surface rather than at the end of the glans.
